Congenital nystagmus, a condition for which there is no consistently effective treatment, causes the eyes to oscillate horizontally whenever these patients attempt to fixate. More than 10,000 Americans have congenital nystagmus, with its consequent, often severe loss of visual function. It is known that their nystagmus diminishes visual acuity, because if it is dampened, in addition to this desired cosmetic effect, there is often an improvement in visual acuity. Recent reports show that feedback (information given) to the patient about eye motion can dampen the nystagmus and improve vision. A technique developed in the applicant's laboratory provided eye position feedback to a congenital nystagmus patient which dampened nystagmus by more than 50 percent. Drawing upon the disciplines of ophthalmology, physiological optics and biomedical engineering, the applicants, in a joint effort, propose to systematically study the efficacy of feedback in an available sample of patients with congenital nystagmus. The investigators will assess feedback's efficacy by determining its effect upon nystagmus, visual acuity, and contrast sensitivity for sinusoidal grating patterns. Specific comparisons of eye position, eye motion and both forms of feedback, when delivered by one or more of three senses, are to be made. A search for a placebo response and evidence of adaptation and habituation are also to be made. The study will estimate what proportion of congenital nystagmus patients are amenable to feedback and how great their improvement in visual function may be. This information will be useful in deciding whether the development of a feedback prosthesis is worthwhile and if it is, how the device should be designed. The project will evaluate the efficacy of a noninvasive technique for the management of congenital nystagmus and at the same time develop specifications for biomedical engineers to use in designing and constructing feedback prostheses for congenital nystagmus patients.